Metal stripping composition and process

ABSTRACT

There is disclosed a chemical stripping solution suitable for removing tin and tin-lead alloys from metallized, e.g. copper coated, substrates so as to leave the said substrate reusable comprising an aqueous solution of hydrogen peroxide in an amount of 0.1 to 10 molar, ammonium bifluoride in an amount of 0.4 to 10 molar, an acid of a type and in an amount such as to maintain the pH of the solution at the surface being stripped below the value at which smut formation occurs whereby effective stripping is achieved in use, and a metal complexing compound in an amount of at least 0.005 molar, the said metal complexing compound comprising 8-hydroxyquinoline or an 8-hydroxyquinoline derivative or a substituted 8-hydroxyquinoline and wherein the molar ratio ammonium bifluoride to complexor is at least 125:1 and the molar ratio of hydrogen peroxide to complexor is at least 50:1.

This invention relates to an improved metal stripping composition andprocess and, more particularly, relates to an improved composition andprocess for stripping tin and tin-lead alloys, such as solders, fromanother metal substrate, such as a copper substrate.

BACKGROUND OF THE INVENTION

Solutions containing hydrogen peroxide have heretofore been proposed foruse in various processes involving the dissolution of metals and metaloxides. Exemplary of these are processes involving pickling, etching,cleaning, chemical brightening or polishing, and the like. Typicaldisclosures of pickling solutions are found in G.B. Patent ApplicationNo. 2,014,552A directed to a solution of hydrogen peroxide and a mineralacid with a saccharin stabilizer and G.B. Pat. No. 1,499,918, and itsequivalent U.S. Pat. No. 4,022,703, directed to a solution of hydrogenperoxide and sulfuric acid with an 8-hydroxyquinoline stabilizer.Typical disclosures of etching solutions are found in G.B. Pat. No.1,474,294, directed to hydrogen peroxide in an aqueous fluoride solutionwith tetrazoliumn as an inhibitor, G.B. Pat. No. 1,295,954 directed toan alkaline solution of hydrogen peroxide containing a metal ioncomplexor and a stabilizer, and G.B. Pat. No. 962,335 directed to asolution of hydrogen peroxide and ammonium fluoride. A typicaldisclosure of a metal cleaner is found in G.B. Pat. No. 1,407,269directed to the use of ferrous sulfate, hydrogen peroxide or nitricacid, sulfuric acid and a bifluoride. Typical disclosures of chemicalbrightening or polishing solutions are found in G.B. Pat. No. 1,209,016,directed to the use of hydrogen peroxide, ammonium bifluoride, oxalicacid and sulfamic acid and in G.B. Pat. No. 1,056,670 directed to theuse of hydrogen peroxide and hydrofluoric acid.

In many of the above-mentioned disclosures, the need for a stabilizerfor the hydrogen peroxide is recognized. In addition to the recognitionin these patents, other disclosures have recognized the general need forstabilization of hydrogen peroxide solutions. Typical of these areFrench Pat. No. 998,486, directed to the use of oxyquinoline compounds,such as the sulfate, and U.S. Pat. No. 3,053,632, directed to the use of2-alkyl substituted 8-hydroxyquinolines.

With the growth of the printed circuitboard industry in recent years,there has been an increasing need for compositions which will strip orremove solder from other metal substrates, such as copper. In themanufacture of printed circuitboards, tin or tin-lead solders arefrequently applied to copper components of the circuitboard, such as theterminal tabs. It is then necessary to remove the solder from the coppersubstrate so that it can be plated with a more noble metal, such asgold. Additionally, there are frequent occurrences of mis-solderingwhich make it necessary to remove the improperly applied solder from thecopper substrate in order to recover the copper plated printed circuitsubstrates for resoldering. In view of the high production rates for theprinted circuitboards, rapid removal of the solder composition isessential. Such removal must, however, be accomplished withoutsignificant attack on the copper substrate.

Attempts to utilize the various hydrogen peroxide based metal treatingcompositions as described above to effect the solder stripping have,generally, not been successful. When used to strip tin and tin/leadalloy solders from copper substrates with these compositions, thestripping rates have been too slow and/or the attack on the coppersubstrates has been too great.

Accordingly, attempts have been made to develop hydrogen peroxide basedsolutions which are particularly adapted for solder stripping. In U.S.Pat. No. 3,841,905, for example, there is described a solder strippingcomposition of hydrogen peroxide and ammonium bifluoride. U.S. Pat. No.3,926,699, which was reissued as Reissue No. 29181, describes a hydrogenperoxide and ammonium bifluoride solder stripping composition whichcontains, as a stabilizer, a combination of Dequest and triisopropanolamine. In G.B. Pat. No. 976,167, there is described a solder strippingcomposition of hydrogen peroxide and fluoboric acid. Another solderstripping composition is described in G.B. Patent Application No.2,074,103A, which composition is made up of hydrogen peroxide, ammoniumbifluoride, trichloroacidic acid and a polyacrylamide. In G.B. Pat. No.1,446,816 or its equivalent U.S. Pat. No. 3,986,970, yet another solderstripper composition is described which is comprised of hydrogenperoxide, an acid, a source of fluoride ions and a stabilizer for thehydrogen peroxide. Among suitable stabilizers disclosed in the patent is8-oxyquinoline. Although these compositions have been used with varyingdegrees of success, they have generally not been able to provide thehigh rates of solder stripping, without attack on the copper substrates,which are presently required in the manufacture of printedcircuitboards.

It is, therefore, an object of the present invention to provide animproved solder stripping composition and process.

A further object of the present invention is to provide an improvedsolder stripping composition and process characterized by high solderstripping rates without significant attack on the metal substrate, suchas copper.

These and other objects will become apparent to those skilled in the artfrom the description of the invention which follows.

SUMMARY OF THE INVENTION

Pursuant to the above objects, it has now been found that a solderstripping composition, having significantly increased stripping ratesand reduced attack on the substrate, can be formulated with hydrogenperoxide, ammonium fluoride or bifluoride, an acid and an8-hydroxyquinoline compound by utilizing these components in certainspecific amounts while maintaining certain specific ratios of thesecomponents to each other. The improved solder stripping composition ofthe present invention is an aqueous solution containing hydrogenperoxide (Component A) in an amount of about 0.1 to about 10 molar,ammonium fluoride or ammonium bifluoride (Component B) in an amount offrom about 0.4 to about 10 molar, an inorganic acid (Component C) in anamount at least sufficient to maintain the pH of the solution at thesurface being stripped below the value at which smut formation occursand, as a metal complexing compound, an 8-hydroxyquinoline compound(Component D) in an amount of at least about 0.005 molar. Additionally,in the composition of the present invention, the molar ratio of hydrogenions to Component D is at least 100:1, and desirably the molar ratio ofComponent A to Component B is at most 1:1, e.g. at most 0.91:1. It isalso desirable that the molar ratio of the ammonium fluoride orbifluoride (B) to the metal complexing compound (D) will be at least125:1 and the molar ratio of the hydrogen peroxide (A) to the metalcomplexing compound (D) will be at least 50:1. When this composition isused, in either a spray or immersion process, and particularly, when itis used with sulfuric acid as a preferred acid in an amount sufficientto maintain the bath pH at a value which is not in excess of about 5.3and is further used with a weight ratio of ammonium bifluoride orfluoride (calculated as ammonium bifluoride) to hydrogen peroxide whichis in excess of about 1.25:1, very rapid stripping of tin and tin/leadsolders from metal substrates, such as copper, is obtained withoutsignificant attack of the copper substrate.

DETAILED DESCRIPTION OF THE INVENTION

The invention aims to provide a chemical stripping solution with highcapacity for tin and tin-lead alloys so that soldered copper substratescan be stripped under spray application conditions as well as immersion.It is also desired for such application conditions that the solutionshould have a high stripping rate. Hydrogen peroxide was chosen as theoxidizing agent because of its high solubility in water which providesthe solution with high stripping capacity. High stripping rate isachieved by using hydrogen peroxide in combination with ammoniumbifluoride or fluoride, with the bifluoride being preferred. However,this combination results in slight dissolution of the copper substrateoccurring and the copper ions thus brought into solution in thestripping composition have a catalysing affect on the decomposition ofthe hydrogen peroxide. Tin and lead ions have little effect on thedecomposition. Investigations have been made, therefore, to try to finda suitable stabilizing agent to prevent decomposition of the hydrogenperoxide or to find a complexing agent to complex the dissolved copperions and prevent their catalytic effect on the decomposition of thehydrogen peroxide. Several chemical compounds were tried in a bathcontaining tin, lead and copper ions and 8-hydroxyquinoline was found tobe an example of a class of compounds which inhibited the decompositionof hydrogen peroxide very effectively. It was found that in the presenceof such compounds as 8-hydroxyquinoline, the copper ions were stronglycomplexed, particularly if the molar ratio of 8-hydroxyquinoline tocopper was higher than one.

The resulting mixture of hydrogen peroxide, ammonium bifluoride and8-hydroxyquinoline type compounds gave a suitably high strippingcapacity for tin and tin-lead alloys and sufficiently good strippingrate but, unexpectedly, a green precipitate thought to be copper8-hydroxyquinoline complex (copper oxinate) was formed and manifesteditself as smut formation on the substrate. It was found that thiscomplex was soluble below pH 5.3, and surprisingly, this problem of smutformation could thus be removed by increasing the acidity of thesolution, as by the addition of sulfuric acid, while this increase inacidity did not increase the rate of stripping of copper form the copperplated printed circuitboard substrate.

Thus, according to the present invention, a chemical stripping solutionsuitable for removing tin and tin-lead alloys from metallized, e.g.copper coated, substrates so as to leave the said substrate reusablecomprises an aqueous solution of hydrogen peroxide in an amount of 0.1to 10 molar, ammonium bifluoride or fluoride in an amount of 0.4 to 10molar, an acid to reduce the pH of the bath to below 5.3 and a metal,e.g. copper, complexing compound in an amount of at least 0.005 molar,the said metal complexing compound comprising 8-hydroxyquinoline or an8-hydroxyquinoline derivative (as defined herein) or a substitute8-hydroxyquinoline.

The hydrogen peroxide is preferably present in an amount of 1 to 6molar, e.g. 2 to 5 molar. The ammonium bifluoride or fluoride ispreferably present in an amount in excess of 0.5 molar, e.g. in therange of 2 to 7 or 3 to 6 molar. The acid is preferably present in therange 0.1 to 4 molar; for example, it may be sulfuric acid which,preferably, is used in the range 1 to 2 molar. The metal complexingcompound is preferably used in the range up to 0.2 molar, e.g. in therange of 0.01 to 0.1 molar or more preferably 0.01 to 0.05 molar. Aparticularly preferred copper complexing agent is 8-hydroxyquinoline.Substituted quinoline in which the substitute is an alkyl or aryl groupattached to one of the carbon atoms of the quinoline molecule are alsoeffective.

References have been made above to stripping tin or solder from coppercoated printed circuitboards for reuse but other stripping purposesbesides this may find use of the present stripping compositionadvantageous. In particular, terminal tabs on printed circuitboards maybecome splashed or coated with solder and this may require to bestripped prior to coating of the terminal tabs with a noble metal suchas gold to ensure that they provide effective contacts for the printedcircuitboards in the electronic apparatus in which the circuitboardswill be used. Here, if the noble metal plating is to be effective, it ishighly desirable that no significant removal of copper occurs whilecomplete removal or substantially complete removal of the tin or solderis achieved.

Ammonium bifluoride is the preferred commercially available source ofhydrofluoric acid but other reactive compositions of ammonia withhydrofluoric acid or salts thereof, such as ammonium fluoride, have alsoproved effective and their use is equally contemplated within the scopeof the present invention. It would appear that the hydrofluoric acid isthe active component and the ammonia appears to have some inhibitingfunction on the hydrofluoric acid in reducing or preventing its attackon the copper. Such other ammonia/hydrofluoric acid salts or mixtures,in addition to ammonium fluoride, which may be used, include mixtures ofammonium halides with hydrofluoric acid.

The hydrogen peroxide is also merely an example of a convenient oxygensource satisfactory to support the reaction of the acid with the solder.While it is the preferred commercially available material, othersuitable oxygen sources could be used and examples of these aretert-butyl hydroperoxide and sodium or ammonium perborate.

So far as the acid for reducing the pH is concerned, sulfuric acid isvery convenient and is preferred but other effective acids would not beexcluded. It is thought, however, that hydrochloric acid may possiblyhave a damaging attack on the copper substrate and it is thus prudent toavoid use of hydrochloric acid.

Various derivates of 8-hydroxyquinoline are also effective, includingthe neutral sulphate of 8-hydroxyquinoline (C₉ H₆ NOH)₂ H₂ SO₄) (alsoknown as ortho hydroxyquinoline), the 8-hydroxyquinoline derivative ofphthalysulphathiazole, 5-sulpho-6-methyl-8-oxyquinoline and8-hydroxy-quinoline-salicylate.

These are the compounds included with the term an 8-hydroxyquinolinederivative (as defined herein).

Specifically preferred stripping compositions comprise 1 to 400, e.g. 10to 200 or 50 to 180 especially 70 to 100 g/l of 100% hydrogen peroxide,at least 1, e.g. 2 to 30, especially 2.5 to 6 g/l of 8-hydroxyquinolinestabilizer, 5 to 350, e.g. 50 to 200, especially 80 to 170 g/l ofsulfuric acid and 20 to 600, e.g. 200 to 400, especially 250 to 350 g/lof ammonium bifluoride.

In addition to using the components described above in amounts withinthe ranges which have been specified, it is also important that certainratios of the various components to each other are also maintained inthe stripping solutions. In this regard, the molar ratio of the ammoniumbifluoride or fluoride compound to the metal complexor should be atleast about 125:1 and preferably within the range of about 125 to about265:1. Additionally, the molar ratio of the hydrogen peroxide oxidizingagent to the metal complexor should be at least about 50:1 and,preferably, is within the range or about 50 to about 115:1.

It has further been found that it is very desirable to maintain theweight ratio of ammonium bifluoride or ammonium fluoride (calculated asammonium bifluoride) to 2-hydrogen peroxide in excess of about 1.25:1.Preferably, this weight ratio is at least about 1.5:1 and, mostpreferably, is from about 1.8 to about 5 (or even higher):1.

With respect to the sulfuric acid used in formulating the compositionsof this invention, as has been noted hereinabove, the amount of sulfuricacid used is desirably sufficient to provide a bath pH which is belowabout 5.3 but which is not sufficiently low as to result in anysignificant increase in the attack of the solution on the coppersubstrate. Most preferably, the amount of sulfuric acid in the solutionis from about 75 to about 185 g/l. Where the bath contains too littleacid, the deposition of green copper oxinate and/or smut formation mayoccur, while excessive attack on the copper may result from using anexcessive amount of acid.

In a most preferred embodiment, it has been found that weight ratios ofthe sulfuric acid to the metal complexor compound which are at leastabout 35:1 produce particularly advantageous results. Most preferably,the weight ratio of sulfuric acid to the metal complexor compound willbe within the range of about 35 to about 95:1.

SPECIFIC EMBODIMENTS OF THE PRESENT INVENTION

The invention may be put into practice in various ways and a number ofembodiments will be described to illustrate the invention with referenceto the following specific examples.

EXAMPLE 1

A formulation for spray stripping of solder (60% tin/40% lead) from acopper layer on a fiberglass resin printed circuitboard substrate wasmade up as follows:

    ______________________________________                                        INGREDIENT         COMPOSITION                                                ______________________________________                                        Hydrogen Peroxide  2.33 Mol (80 g/l)                                          (100%)                                                                        Ammonium bifluoride                                                                              5.25 Mol (300 g/l)                                         Sulfuric Acid      1.4 Mol (138 g/l)                                          8-hydroxyquinoline 0.021 Mol (3.0 g/l)                                        Water              to 1 liter                                                 ______________________________________                                    

The ingredients for this composition were mixed together in the ordergiven and a resin printed circuitboard carrying a copper layer 40mincrons thick with a layer of solder 20 microns thick was contacted byspraying the above composition at a net rate of about 25 cc per squarecentimeter of solder-covered surface per minute at a temperature of 25°C. Net rate means the actual amount of liquids sprayed which contact thesurface being stripped. The composition had a pH of 4.0. The solder wassubstantially removed within 1 minute with no significant attack and nomeasurable reduction of thickness of the copper layer. This rate ofattack did not substantially diminish until 10 cc of solution had beenused to strip 32 square centimeters of printed circuit board. Analysisof the stripping composition at this state, i.e. after stripping of 3200square centimeters of printed circuit board by 1 liter of solutionindicated that the bath contained 32 g/l of tin, 21 g/l of lead (ofwhich the larger amount was precipitated as sulphate of fluoride) and1/3 g/l of copper.

In accordance with the present invention, one has to make certain thatthe pH at the surface being stripped remains below that at which smutformation occurs (5.3 in the case of copper). Thus the presence ofhydrogen peroxide in the stripping reaction causes the pH to tend torise during stripping as compared with the pH of the bulk solution andtherefore one needs to make certain that the initial pH of the bulksolution is at such level that in use the pH at the surface will notrise above the critical pH value. For copper it has been found that aninitial pH of not more than 4.0 produces an effective system in whichsmut formation is avoided.

EXAMPLE 2

A bath similar to Example 1 was made up in the same way except that thehydrogen peroxide concentration was 1 Molar, sulfuric acid concentration1 Molar, and the 8-hydroxyquinoline concentration 0.02 Molar. The bathwas used under the same conditions as described for Example 1 andsimilar results were obtained.

EXAMPLE 3

A bath similar to Example 1 was made up in the same way except that thehydrogen peroxide concentration was 4.5 Molar (153 g/l), sulfuric acidconcentration 2 Molar (164 g/l), the 8-hydroxyquinoline concentration0.04 Molar (5.84 g/l) and the ammonium bifluoride concentration 5 Molar(285 g/l). The bath was used under the same conditions as described forExample 1 and similar results were obtained.

EXAMPLE 4

The pickling effect of a chemical stripping solution in accordance withthe present invention were compared with a solution, similar to thosedisclosed in U.K. Patent Specification No. 1,499,918, made up asfollows:

    ______________________________________                                        Solution A                                                                    Ingredient         Composition                                                ______________________________________                                        Hydrogen Peroxide  0.58 Mol (20 g/l)                                          Sulfuric Acid      0.92 Mol (90 g/l)                                          8-hydroxyquinoline 0.0007 Mol (0.1 g/l)                                       Water              to 1 liter.sub.2                                           ______________________________________                                    

A copper laminate printed circuitboard immersed in the solution ofExample 1 for one minute was compared with an identical board immersedin Solution A for one minute. Moderate magnetic agitation was used inboth cases. After this treatment the appearances of the two boards weresimilar in that the copper surfaces were clean and both were slightlyetched/attacked/pickled. However, it was found that wereas Solution Aremoved copper at a rate of more than 0.9 um/min, the solution ofExample 1 removed copper only at a rate of 0.09 um/min.

EXAMPLE 5

The solder stripping properties of a chemical stripping solution inaccordance with the present invention was compared with Solution A asset out in Example 4, above. A resin printed circuitboard carrying acopper layer 40 microns thick with a layer of solder 20 microns thickwas immersed in a quantity of Solution A. Under moderate magneticagitation, no marked stripping of solder was observed. Secondly, aprinted circuitboard was subjected to the spray treatment as describedin Example 1 except that Solution A was used instead of the solution ofExample 1. A stripping rate of 0.7 um/min was observed as compared to astripping rate of 14 um/min when the solution of Example 1 was used.

To further illustrate the operation of the present invention, additionalstripping solutions were formulated in accordance with Table I, below.As used in this table, ingredient A is H₂ O₂, ingredient B (except asotherwise indicated) is NH₄ HF₂, ingredient C is H₂ SO₄, and ingredientD is 8-hydroxyquinoline.

                  TABLE I                                                         ______________________________________                                        INGREDIENT G/L A        B       C    D                                        ______________________________________                                        6               2        5*      50  10                                       7               2        5       50  10                                       8              80       300     138  3                                        9              80       300*    138  3                                        10             34       300      98  3                                        11             153      285     164  5.84                                     12             80       196**   138  3                                        13             80       196**   184  3                                        ______________________________________                                         *NaF was substituted for NH.sub.4 HF.sub.2                                    **NH.sub.4 F was substituted for NH.sub.4 HF.sub.2                       

In the foregoing examples, example 6 corresponds to Example 12 of G.B.Pat. No. 1,446,816. Additionally, a usable solution was not obtained inExample 9 because of the insolubility of the sodium fluoride at thelevel specified.

Each of the formulations of Examples 6 through 8 and 10 through 13 weretested for the rate of stripping 60/40 tin/lead solder, using boards asdescribed in Example 5, by spraying as described in Example 1 and byimmersion as described in Example 5. Additionally, these formulationswere tested for attack on the copper substrate, using copper platedboards as described in Example 4, the test being carried out both byimmersion, as in Example 4, and by spraying in which the test panel wasoscillated through a 3 cm diameter cone of spray. Finally, theformulations of these examples were tested for redeposition of solder onthe copper substrate after stripping, using both immersion and spraying,as in Example 5, but utilizing boards having a slightly thinner solderlayer than those of Example 5. The results of these tests are set forthbelow in Table II for the spray testing and in Table III for theimmersion testing.

                  TABLE II                                                        ______________________________________                                                SOLDER        COPPER     APPEAR-                                      PROPER- STRIPPING     ATTACK     ANCE                                         TY EX-  RATE MICRONS/ MICRONS/   OF COPPER                                    AMPLE   MINUTE        MINUTE     SURFACE (1)                                  ______________________________________                                        6       1.3           0.19       A                                            7       0.8           0.39       A                                            8       19.3          0.58       B                                            10      16.4          0.09       B                                            11      16.5          1.17       B                                            ______________________________________                                         NOTES ON TABLE II                                                             (1) A; GREY SMUT B; NO SMUT C; GREEN COPPER OXINATE                      

                  TABLE III                                                       ______________________________________                                                SOLDER        COPPER     APPEAR-                                      PROPER- STRIPPING     ATTACK     ANCE                                         TY EX-  RATE MICRONS/ MICRONS/   OF COPPER                                    AMPLE   MINUTE        MINUTE     SURFACE (1)                                  ______________________________________                                        6       0.62          0.035      A                                            7       0.62          0.10       A                                            8       11.4          1.579      A                                            10      10.0          0.33       C                                            11      12.9          1.43       B                                            12      11.1          1.09       B C                                          13      7.1           5.8        B                                            ______________________________________                                         NOTES ON TABLE III                                                            (1) A; GREY SMUT B; NO SMUT C; GREEN COPPER OXINATE                      

Additional stripping solutions were formulated in accordance withExample 8, above, with the exception that the amount of the ammoniumbifluoride in the solution was varied. These solutions were then testedfor the solder stripping rate and the copper attack by spraying inaccordance with the procedures set forth hereinabove. The compositionsof the formulations used and the results obtained are set forth in TableIV.

    ______________________________________                                                 AMOUNT    SOLDER        COPPER                                                OF        STRIPPING     ATTACK                                       PROPERTY NH.sub.4 HF.sub.2                                                                       RATE MICRONS/ MICRONS/                                     EXAMPLE  G/L       MINUTE        MINUTE                                       ______________________________________                                        14       25        2.4           1.0                                          15       50        3.0           0.6                                          16       100       2.8           0.5                                          17       150       10.9          0.4                                          18       200       10.5          0.4                                          19       250       12.7          0.4                                          20       300       19.5          0.4                                          21       400       26.8          0.3                                          ______________________________________                                    

In none of the foregoing examples 14 through 21 was there any evidenceof smut formation on the copper surface after stripping.

What is claimed is:
 1. A chemical stripping composition suitable forremoving tin and tin-lead alloys from a metallized substrate which is anaqueous solution comprising:A. hydrogen peroxide in an amount of fromabout 0.1 to about 10 molar, B. ammonium bifluoride or ammonium fluoridein an amount of from about 0.4 to about 10 molar, C. an acid in anamount such as to maintain the pH of the solution at the surface beingstripped below the value at which smut formation occurs or compounds ofthe metal of the metallized surface and the metal complexing compoundare deposited on the metallized surface, and D. a metal complexingcompound which is an 8-hydroxyquinoline compound in an amount of atleast 0.005 molar, andwherein the molar ratio of component B tocomponent D is at least 125:1 and the molar ratio of component A tocomponent D is at least 50:1.
 2. The composition as claimed in claim 1wherein component B is ammonium bifluoride, component C is sulfuric acidand component D is 8-hydroxyquinoline.
 3. The composition as claimed inclaim 2 wherein the molar ratio of component B to component D is fromabout 125-265:1 and the molar ratio of component A to component D isfrom bout 50-115:1.
 4. The composition as claimed in claim 2 wherein theweight ratio of component B to component A is in excess of about 1.25:1.5. The composition as claimed in claim 3 wherein the weight ratio ofcomponent B to component A is from about 1.8-5.0:1.
 6. The compositionas claimed in claim 4 wherein the weight ratio of component C tocomponent D is in excess of about 35:1.
 7. The composition as claimed inclaim 5 wherein the weight ratio of component C to component D is fromabout 35-95:1.
 8. The composition as claimed in claim 2 whereincomponent A is present in an amount from about 1 to about 6 molar,component B is present in an amount from about 2 to about 7 molar,component C is present in an amount from about 0.1 to about 4 molar, andcomponent D is present in an amount from about 0.01 to about 0.1 molar.9. The composition as claimed in claim 7 wherein component A is presentin an amount from about 50 to about 180 g/l, component B is present inan amount from about 250 to about 350 g/l, component C is present in anamount from about 80 to about 170 g/l, and component D is present in anamount from about 2.5 to about 6 g/l.
 10. A process for stripping tinand tin-lead alloy solders from a metallized substrate which comprisescontacting the solder coated substrate with the composition of claim 1for a period of time sufficient to remove substantially all of saidsolder without significant attack on said substrate.
 11. The process asclaimed in claim 10 wherein component B is ammonium bifluoride,component C is sulfuric acid and component D is 8-hydroxyquinoline. 12.The process as claimed in claim 11 wherein the molar ratio of componentB to component D is from about 125-265:1 and the molar ratio ofcomponent A to component D is from about 50-115:1.
 13. The process asclaimed in claim 11 wherein the weight ratio of component B to componentA is in excess of about 1.25:1.
 14. The process as claimed in claim 12wherein the weight ratio of component B to component A is from about1.8-5.0:1.
 15. The process as claimed in claim 13 wherein the weightratio of component C to component D is in excess of about 35:1.
 16. Theprocess as claimed in claim 14 wherein the weight ratio of component Cto component D is from about 35-95:1.
 17. The process as claimed inclaim 11 wherein component A is present in an amount of from about 1 toabout 6 molar, component B is present in an amount of from about 2 toabout 7 molar, component C is present in an amount from about 0.1 toabout 4 molar, and component D is present in an amount from about 0.01to about 0.1 molar.
 18. The process as claimed in claim 16 whereincomponent A is present in an amount from about 50 to about 180 g/l,component B is present in an amount from about 250 to about 350 g/l,component C is present in an amount from about 80 to about 170 g/l, andcomponent D is present in an amount from about 2.5 to about 6 g/l.
 19. Achemical stripping composition suitable for removing tin and tin-leadalloys from a metallized substrate which is an aqueous solutioncomprising:A. hydrogen peroxide in an amount of from about 0.1 to about10 molar, B. ammonium bifluoride or ammonium fluoride in an amount offrom about 0.4 to about 10 molar, C. an acid in an amount such as tomaintain the pH of the solution at the surface being stripped below thevalue at which smut formation occurs or compounds of the metal of themetallized surface and the metal complexing compound are deposited onthe metallized surface, and D. a metal complexing compound which is an8-hydroxyquinoline compound in an amount of at least 0.005 molar,andwherein the molar ratio of hydrogen ions to component D is at least100:1.
 20. The composition as claimed in claim 19 wherein the molarratio of component A to Component B is at most 1:1.